Application of OE in Diagnosis of EGC

Inclusion Criteria: Meet item 1or 2 + any items of 3-7 1. Male ≥ 40 years old, female ≥ 50 years old. 2. More than one year since the last gastroscopy. 3. Patients from the areas with high incidence of stomach cancer (Shandong Province, Liaoning Province, Fujian Province, Gansu Province, Qinghai Province, Ningxia Province, Jilin Province, Jiangsu Province, Shanghai). 4. Patients with pre-cancerous gastric diseases such as chronic atrophic gastritis, gastric ulcer, gastric polyp, hypertrophic gastritis, pernicious anemia, etc. in the past. 5. First-degree relatives of patients with a family history of gastric cancer. 6. Other high-risk life factors for gastric cancer (high salt, pickled diet, smoking, heavy alcohol consumption, etc.) 7. Positive serum gastric function tests (GastroPanel) include: H. pylori (H.P) antibody （+）, Fasting pepsinogen I and II ratio (PG I/PGII) \<3.89, gastrin 17 (G-17) \>1.50 pmol/L. Exclusion Criteria: 1. Patients who have undergone invasive treatment such as surgical resection, PEG, chemotherapy etc. of either stomach or oesophagus. (except for EMR and ESD). 2. Patients with a confirmed diagnosis of progressive cancer above T2 degreed according to the TMN classification of cancer。 3. Patients on anticoagulants that cannot be biopsied. 4. Patients who have undergone gastrectomy. 5. Patients who have taken PPIs or H2 receptor antagonist within two weeks. 6. Patients with history of malignant neoplasm; high suspicion of neoplasm; severe cardiac, pulmonary, hepatic or renal insufficiency; severe mental illness and pregnant women. 7. Patients who did not signed the consent form.